1. Field of the Invention
The present invention is directed to a bulk material, a coating and a process for making the same wherein the coating and the bulk material are antifouling (adhesion resistant), nontoxic and robust materials (e.g. chemically, thermally and mechanically suited to prolonged use in sea water). More particularly, the bulk material, the coating and the process of the presently disclosed invention involve the formation of an exterior layer which inhibits and/or decreases the rate of growth and/or attachment of marine organisms and/or marine plant life to the exterior layer when submerged in water (especially for prolonged periods of time). The polymer of the presently disclosed invention (either as a bulk material or as a coating) has a nontoxic surface which is minimally attractive to the settlement of marine organisms and plants.
2. Description of the Related Art
Most surfaces (if not all) immersed in the sea become covered with marine organisms. The diversity of these organisms and the environments in which they live create complex problems which any useful antifouling coating must overcome. The problem is most acute for ships. Fouling organisms (organisms that attach to surfaces such as exterior ship hulls exposed to sea water) add weight, increase hydrodynamic drag, increase fuel consumption, facilitate corrosion of the hull and decrease speed, maneuverability and range.
Toxic coatings containing metals have been the technology of choice to prevent fouling. Although effective on a broad range of fouling organisms, these metals are also toxic to non-target animals and plants. Unintended mortality of fish and shellfish (in particular) is an undesirable toxic characteristic of these antifouling coatings containing metals. Compounds containing arsenic, cadmium, lead and mercury are now proscribed. Presently, tin containing antifouling compounds are still used in restricted circumstances and copper compounds are still used widely. However, environmental authorities around the world have expressed their intent to ban paints containing high levels of copper and tin and move quickly toward the use of nontoxic antifouling compounds as soon as effective substitutes become available.
Organic polymers have been used as binder resins in antifouling coatings. In order to impart the durability needed for prolonged underwater service, these resins possess a high proportion of polar functional groups such as esters (--COOR) and ethers (R--O--R'). These polar funcitonal groups, however, provide a polar surface well suited for bonding to, for example, barnacles, limpets, diatoms, grass and other marine organisms.
Other organic polymers such as polyethylene {--(--CH.sub.2 CH.sub.2).sub.m --} or polypropylene {--(--CH(CH.sub.3)--CH.sub.2 --).sub.m --} are constructed entirely from nonpolar functional groups wherein m is a positive integer. However, while these materials bond weakly to marine organisms, they also bond weakly to underlying paint layers and also lack the thermal and mechanical stability needed for extended immersion in water. In addition, because these nonpolar functional group organic polymers are not dissolved, softened or even wetted by conventional solvents, it is extremely difficult to lay these polymers down as a smooth, nonporous film. Being porous, these polymers are susceptible to penetration of adhesives from marine organisms wherein a strong physical bond is formed with such an organic polymer even when chemical incompatibility is present.